Heat and solvent resistant flexible gasket means and process for production thereof

ABSTRACT

There is provided a novel form of heat and solvent resistant gasket means available in strip and, where desired, ring form comprising a compacted fibrous core surrounded by a flexible metallic winding, said winding being further surrounded by fibrous heat resistant material impregnated with heat and solvent resistant polymer to provide a smooth outer surface for said gasket means. The gasket means may optionally further include a central metallic core within the fibrous core and also include a second flexible metallic winding substantially coaxial with said first metallic winding.

This is a division of application Ser. No. 798,167, filed 05/18/77, nowU.S. Pat. No. 4,119,323.

RELATED APPLICATIONS

This application claims priority from Applicant's Swiss application6222/76 of 18 May 1976.

BACKGROUND OF THE INVENTION

Where, in a machine, it is necessary to join two portions thereof inorder to prevent the passage through said joints of a fluid or gaseousmedium, the mode of sealing will depend on whether the two parts of themachine move in relationship to each other or are static in relationshipto each other once the machine is assembled. Where the machine partsmove relative to each other, for example, in an automobile piston movingin an automobile cylinder, the sealing problem is designated as dynamicsealing. On the other hand, where, in a similar machine, the cylinderhead is connected to the cylinder block, the two parts do not moverelative to each other and the sealing is designated as static sealing.It is with this latter form of sealing that the present invention isconcerned. In most, although not all, modes of static sealing, there areutilized gasket means which are substantially annular in plan view andhave a predetermined generally, but not exclusively, circular crosssection. A prime example of this type of gasket means is the "0" ring.Such gasket means are employed in the sealing of flanges, lids,stoppers, screws, and the like.

For static sealing, one may also employ substantially flat gasket meansas, for example, the gasket means employed between the head and theblock of an automobile cylinder. While these means are available for theprovision of sealing against higher pressures, they employ substantiallyharder and less elastic sealing materials, and require a high initialstressing force which necessarily leads to greater expenses.

On the other hand, where 0-rings are used, in so far as they aresufficiently elastic, only minimal initial stressing forces arerequired, and they automatically form themselves into a sealing pattern.The advantage of the 0-ring type of sealing means is that as thepressure in the contained volume rises, the gaseous or fluid mediumpressing on the exposed surface of the 0-ring automatically transfersthe pressure onto the working faces of the mutually abutting surfaces ofthe equipment. Since the sealing rings have, because of their nature, aradial or axial initial stress, the sealing force will always exceed theforce exerted by the gaseous or liquid medium.

The 0-rings utilized heretofore have usually been made of rubber orother elastomers of varying qualities and hardnesses which have,unfortunately, the common disadvantage that they have a relatively shortworking life. This working life is shortened by higher temperatures,particularly in the presence of air, which "age" the rubber or elastomerpartly through oxidation and partly through further vulcanization. Thesetwo factors increase the hardness of the gasket means and, at the sametime, reduce the elasticity and flexibility thereof leading, ultimately,to rupture. Elastomeric 0-rings must, therefore, be periodicallyreplaced. Where the sealing of dangerous media is concerned, for safetyreasons, the replacement must be carried out at intervals which are soshort that no problems of ageing in the gasket means can be allowed tohave appeared.

Furthermore, there are certain circumstances under which the utilizationof elastomeric gasket means is not permissible. These circumstancesinclude, for example, very low temperatures--that is to say, below minus60° C.--or very high temperatures--that is to say, above about 200°C.--in the presence of chemically active substances which attack theelastomeric material or, more recently, radioactive media.

It would therefore be desirable to provide a gasket sealing means forstatic sealing in strip or suitably ring form, the elasticity of whichdoes not deteriorate through ageing, which is utilizable up to 500° C.,and which is substantially unaffected by even strong radioactiveradiation.

SUMMARY OF THE INVENTION

There is provided a gasket sealing means in strip or ring form, saidstrip or ring having a predetermined cross section, comprising achemically and temperature resistant mass having imbedded therein aradial and/or axially spring elastic winding. There is further provideda process for the manufacture of such gasket means. The invention hereofcomprises a preformed substantially heat and solvent resistant gasketsealing means of predetermined cross section comprising a core ofcompacted heat resistant fibrous material. In one embodiment of theinvention, said core surrounds a metallic core embedded substantiallyaxially therein. This central core is surrounded by a flexible,substantially helical, metallic winding and said winding itself isenveloped by a further envelope of compacted heat resistant fibrousmaterial. Said envelope is impregnated with a heat and solvent resistantmaterial, suitably a polymeric material, in sufficient quantity to bindthe fibers into an unitary envelope and provide a substantially smoothouter surface upon said envelope. In a further embodiment of theinvention, a predetermined length of the thus provided gasket means isjoined together at its ends to provide an 0-ring type gasket. In apreferred embodiment of this 0-ring, a flexible spring is insertedsubstantially axially into each of the aforesaid ends prior to sealingsaid ends together whereby there is provided additional structuralstrength to the joint.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially exploded plan view of one of the preferredembodiments of the present invention.

FIG. 2 is a cross sectional view of FIG. 1 viewed at 2--2.

FIG. 3 is a cross sectional view of a strip of FIG. 1 formed into an0-ring.

FIG. 4 is a cross sectional view of a further embodiment similar to theview of FIG. 2 comprising a device having two coaxial sheaths.

FIG. 5 is a cross sectional exploded view of the portion of the view ofFIG. 3 at joint 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The basic embodiment of the present invention comprises, as illustratedin FIG. 2, a central core of fibrous material 3, a flexiblesubstantially helical metallic winding 2, surrounding said core, anouter envelope 5, also of heat resistant fibrous material, impregnatedwith a heat resistant polymeric material in a sufficient amount toprovide a smooth envelope 6 surrounding the entire gasket sealing means.

In the preferred embodiment of the invention, the central core comprisesheat resistant fibers. Such fibers may be asbestos, quartz, fiberglass,

or the like,

or they may be synthetic fibers--for example, polytetraflor-ethylene,

or the like.

The central core may comprise said fibers compressed into a column,woven into a string, or initially woven into fine strands, and saidstrands further woven into a woven core of substantially cylindricalcross section.

In one of the preferred embodiments of this invention, as illustrated inFIG. 1, there is provided a metallic core running substantially axiallythrough the fiber core. This metallic core may be provided from any highmelting metal. Steel, nickel chromium steel, or nickel itself isconsidered suitable; however, the invention is in no way limitedthereto.

In a further preferred modification of the present invention, the metalcore 4 is integrally bound to the surrounding fiber core 3.

Nothing herein should be considered as limiting the invention to the useof a single monomer. The use of co-monomers for the product ofco-polymers is considered to be within the scope of the presentinvention.

As impregnating melt polymers there may be employedpolytetrafluoroethylene, silicones, Viton (Dupont) and combinationsthereof.

The polymerization conditions for said monomers and co-monomers areconsidered to be well known to those skilled in the art.

The fiber core 3 is then surrounded with a helical metallic winding 2.The metallic winding 2 is formed of flexible metal having springqualities, suitably spring steel. The winding may be in the form of ahelically wound strip as shown in FIG. 1 or in the form of a moreconventional round, or substantially round, spring wire rather than astrip. It is also within the purview of the present invention that thewinding may utilize the so-called coiled coil format generallyencountered in incandescent lamps wherein a thin wire is tightly coiledupon itself to form a very flexible coil and this tightly wound coil isthen helically wound around core 3 in the manner of strip 2.

Around the helical winding 3 there is provided a further layer offibrous material 5. The same fibrous materials utilized in the formationof core 3 may be employed. It is not necessary, however, that theidentical fiber be used for the provision of inner core 3 and outercovering 5. Said outer covering 5 is similarly impregnated with a heatand solvent resistant polymeric material in such a way as to provide asmooth envelope 6 surrounding the fibrous covering 5. This polymericimpregnate may be any of those utilized to impregnate the inner core 3but need not necessarily be identical to the one utilized in theimpregnating inner core 3. In a further embodiment of the invention, anintermediate metallic winding 12 is located coaxially with winding 2imbedded in fibrous covering 5.

In one of the preferred embodiments of the present invention, the gasketmeans is provided in the form of an 0-ring. Said 0-ring comprises apredetermined length of the gasket means, the exposed ends whereof havebeen sealed together. In an especially preferred embodiment of said0-ring gasket, there is provided a spring means axially embedded in eachend to provide a metallic bridge between the two ends of the originalpiece of gasket means material. In the process of preparing the gasketmeans of the present invention, the fibrous core 3 is, preferably, boundto the metallic core 4 by impregnating said fiber core with a suitabletemperature resistant, substantially insoluble, polymeric material. Suchimpregnation may take place by passing the core through a melt of thepolymer or by passing it through a mixture containing one or moremonomers, and then subjecting the monomer saturated core topolymerization conditions which may be internal or external; thus, thecore may be soaked in a monomer which polymerizes upon exposure to heat,air, moisture, radiation, or free radical sources.

The metallic winding 2 is then placed around the core 3. This may beachieved in one of two ways. In one approach there is preformed ahelical winding 2 through which the core 3 is drawn. Where it is desiredto produce substantial lengths of the gasket material, however, it ispreferred to wind the helical spring 2 around the core material usingspring winding equipment which is well known to those skilled in theart.

The outer covering 5 is then placed upon the metallic winding 2. Whilethis may be done by drawing a preformed sleeve of previously woven fibermaterials over the metallic winding, it is, again, generally preferredto weave or knit the fibrous material around the metallic winding in amanner well known in the art--in particularly, in the art of cablemanufacture. It is especially preferred to utilize fibers which havepreviously been spun into fine thread to provide the smoothest possiblecoating of whatever thickness desired upon the metallic winding.

If desired, a second metallic winding 12 may then be placed uponcovering 5 in a similar manner to that set forth above, and a furthercovering 15 also of fine spun fibrous material placed upon said secondwinding 12. The fibrous envelope 5, 15, or both, are then impregnatedwith a heat and solvent resistant polymer in the manner set forth above.In this case, however, it is desirable to provide a smooth outer surfacein order to facilitate the sealing function of the product. This smoothenvelope may be provided either by carrying out the polymerization ordeposit the impregnation within a mold of predetermined cross sectionwith respect to diameter and shape or, preferably, drawing the coatedand impregnated product through one or more dyes of suitable size andshape. Where quantity production is in view, this latter mode is to bepreferred.

While the present invention should in no way be considered as limitedthereto or thereby, it has been found that for the provision of thewinding 2 strips of string steel of 0.2 to 0.5 millimeters inwidth/thickness are to be preferred.

There are readily provided by the above identified procedures gasketsealing means having a cross sectional diameter of between 2.75 and 12millimeters (This refers, of course, to the sealing material itself andnot to the "cross-0" diameter of annular 0-rings which are also withinthe purview of the present invention).

The products of the present invention have an elasticity of the sameorder of magnitude as the elastomeric 0-rings presently known in theart, but with the advantage that the 0-rings (and other forms of saidgasket sealing means, within the purview of the present invention) donot age and have a "in use" life of approximately twenty-five times thatof the conventional elastomeric 0-rings while, at the same time, beingstable at temperatures up to 500° C. and are resistant to pressures ofup to twenty-five atmospheres as well as to attack by oils, benzenes,oxygenated and unoxygenated hydrocarbons, acids, alkalis, and otherchemically aggressive materials. The materials produced by the presentinvention are also resistant to high levels of radioactivity and,therefore, despite their substantially higher initial cost compared tothe estomeric rings, are, because of their greater active life,especially to be recommended in the construction of atomic reactors.

Where there are utilized, in the outer envelope 5 or 15, quartz fibersin the form of windings or weavings, the products of the presentinvention are temperature resistant up to 1500° C.

I claim:
 1. A process of forming a substantially heat and solventresistant gasket sealing means comprising the steps of(a) compactingfibrous material around a metallic core; (b) impregnating said core witha binding material whereby said fibrous material adheres substantiallyand inseparably to said metallic core to form a composite core; (c)surrounding said composite core with a flexible substantially helicalmetallic winding; (d) winding fibrous material in woven form around saidmetallic winding to provide a fibrous sheath therefor; (e) impregnatingthe said fibrous sheath with a substantially heat and solvent resistantpolymeric material in an amount sufficient to provide an envelope havinga smooth surface.
 2. A process according to claim 1 additionallycomprising sealing a predetermined length of the device of claim 1 intoan annular ring of predetermined diameter.
 3. A process of claim 1comprising the additional steps of(f) cutting a predetermined length ofthe means of claim 1 to provide a strip thereof; (g) introducing a firstend of a spring into one end of said strip and introducing a second endof said spring into the other end of said strip thereby connecting theends of said strip; (h) filling any remaining space between the ends ofsaid strip with fibrous material; (i) impregnating said thus introducedfibrous material with a heat and solvent resistant polymeric sealant toprovide a smooth joint between the ends of said strip to provide anannular ring of predetermined diameter.
 4. A process of claim 1 in whichstep (c) comprises drawing the composite core of step (b) through apreformed winding.
 5. A process of claim 1 in which step (c) compriseswinding said metallic winding around said composite core.
 6. A processof claim 1 additionally comprising intermediate steps of (d')surrounding said fibrous sheaths of step (d) with a second metallicwinding and (d") surrounding said second metallic winding with a secondfibrous sheath in the manner of step (d).
 7. A process of claim 3additionally comprising intermediate steps of (d') surrounding saidfibrous sheaths of step (d) with a second metallic winding and (d")surrounding said second metallic winding with a second fibrous sheath inthe manner of step (d).